Effect of mild medical hypothermia on in vitro growth of Plasmodium falciparum and the activity of anti-malarial drugs

Khalid Rehman, Ulrich Sauerzopf, Luzia Veletzky, Felix Lötsch, Mirjam Groger, Michael Ramharter

Cerebral malaria remains a medical emergency with high mortality. Hypo-perfusion due to obstructed blood vessels in the brain is thought to play a key role in the pathophysiology of cerebral malaria leading to neurological impairment, long-term neuro-cognitive sequelae and, potentially, death. Due to the rapid reversibility of vascular obstruction caused by sequestered Plasmodium falciparum, it is hypothesized that mild medical hypothermia-a standard intervention for other medical emergencies-may improve clinical outcome. This preclinical in vitro study was performed to assess the impact of mild hypothermia on parasite growth and the intrinsic activity of anti-malarials drugs. Three laboratory-adapted clones and two clinical isolates were used for growth assays and standardized drug sensitivity assessments using the standard HRP2 assay. All assays were performed in parallel under normothermic (37 °C), mild hypothermic (32 °C), and hyperthermic (41 °C) conditions. Parasite growth was higher under standard temperature condition than under hypo- or hyperthermia (growth ratio 0.85; IQR 0.25-1.06 and 0.09; IQR 0.05-0.32, respectively). Chloroquine and mefloquine had comparable in vitro activity under mild hypothermic conditions (ratios for IC50 at 37 °C/32 °C: 0.88; 95 % CI 0.25-1.50 and 0.86; 95 % CI 0.36-1.36, respectively) whereas dihydroartemisinin was more active under mild hypothermic conditions (ratio for IC50 at 37 °C/32 °C: 0.27; 95 % CI 0.19-0.27). Hyperthermia led by itself to almost complete growth inhibition and precluded further testing of the activity of anti-malarial drugs. This preclinical evaluation demonstrates that mild medical hypothermia inhibits in vitro growth of P. falciparum and enhances the pharmacodynamic activity of artemisinin derivatives. Based on these preclinical pharmacodynamic data, the further clinical development of mild medical hypothermia as adjunctive treatment to parenteral artesunate for cerebral malaria is warranted.